VENTILATION. 


BY  HENRY  B.  BAKER,  M.  D.,  SECRETARY  OF  STATE  BOARD  OF  HEALTH, 

LANSING,  MICH. 


[  Reprinted  from  the  Annual  Report  of  the  Michigan  State  Board  of  Health  for  the  fiscal  year  1894.] 


[  Reprint  No.  459.] 

Mr.  President,  Ladies  and  Gentlemen:  *In  the  time  allotted  to 
me,  I  propose  to  suggest  some  of  the  general  facts  and  principles  which 
need  to  be  understood  by  all  who  have  to  do  with  the  subject  of 
ventilation. 

These  general  facts  and  principles  may  be  profitably  studied  in  groups, 
as  follows : 

1.  Facts  relating  to  the  constant  needs  of  the  living  body  for  unbreathed 
air. 

2.  Faots  relating  to  air  and  its  movements  with  reference  to  the  parti¬ 
cles  whioh  constitute  the  specific  causes  of  diseases. 

3.  Faots  relating  to  the  oauses  of  movements,  and  the  rates  of  move¬ 
ment  of  air. 


Quantity  of  Air  Needed  for  Respiration. 

1.  In  the  first-mentioned  group  is  the  well-known  faot  that  unless 
fresh  air  is  supplied  to  the  human  body,  life  is  not  sustained.  Fresh  air 
is  needed  to  supply  the  body  with  oxygen  which  is  consumed  in  the  vital 
processes  whioh  yield  the  forces  and  motions  which  constitute  the  phe¬ 
nomena  of  life.  Fresh  air  is  needed  also  to  displace,  drive  away,  and 
remove  produots  of  vital  aotion,  which,  if  allowed  to  remain  in  the  body, 
poison  it  and  lead  toward  death. 

How  much  fresh  air  is  needed?  Those  who  have  studied  this  subject 
have  generally  agreed  that  about  2,000  cubio  feet  of  fresh  air  per  hour  is 
a  fair  allowance  for  each  person ;  and  as  the  vital  processes  of  children  are 
more  rapid  than  those  of  adults,  I  believe  that  school  children  should 
have  as  much  as  adults. 

There  is  a  common  fallacy  that  in  a  large  room  a  less  quantity  of  air 
per  hour  is  sufficient.  That  is  true  only  for  the  very  short  time  until  the 
air  of  the  room  has  been  once  used.  However,  the  ruom  should  be  large 
enough  to  allow  at  least  twenty-five  square  feet  of  floor  space  to  each 
pupil  or  person ;  and  high  enough  to  allow  at  least  six  hundred  oubio 
feet  of  air  space  to  each  pupil  or  person.  One  reason  for  this  is  that  in  a 
less  spaoe  per  person  the  requisite  quantity  of  air  cannot  be  moved 
through  the  spaoe  without  causing  drafts  which  are  dangerous  to  health. 
Just  how  drafts  cause  sickness  may  not  be  fully  dealt  with  here  and  now; 
but  that  drafts  do  oause  sickness  has  been  abundantly  proved.  In  order 
to  prevent  drafts  the  space  allowed  for  each  occupant  of  a  room  must  not 
be  less  than  as  just  stated. 


♦This  was  a  paper  read  at  the  Sanitary  Convention  held  at  Hillsdale  in  July,  1893. 


cxxx  STATE  BOARD  OF  HEALTH.— REPORT  OF  SECRETARY,  1894. 


Proper  Location  of  Foul-air  Outlets. 

2.  Kecent  progress  in  sanitary  soience  has  demonstrated  the  fact  that 
many  diseases,  now  known  as  “speoific,  ”  are  caused  by  living  organisms, 
microsoopic  in  size,  but  particulate,  having  weight,  being  capable  of  set¬ 
tling  as  dust  upon  floors  and  artioles  in  inhabited  rooms.  In  the  human 
body,  there  seem  to  be  many  natural  protections  against  the  inhaling  of  such 
dangerous  particles.  In  the  first  place  the  normal  nose  is  so  formed  as 
greatly  to  avoid  catching  dust  particles  which  being  heavier  than  air  have 
a  downward  motion — the  normal  nostrils  do  not  open  upward,  they  open 
downward.  In  the  next  place,  the  opening  of  such  nostril  is  generally 
protected  by  fine  hairs,  which,  being  moistened  by  the  air  exhaled,  tend 
to  catch  and  prevent  the  entrance  of  dust.  Thirdly,  normal  secretions  of 
the  membranes  of  the  nose  and  throat  tend  to  stop  the  further  entrance 
of  particles;  and  the  nasal  mucus  has  power  to  destroy  at  least  some  of 
the  germs  of  disease.  Notwithstanding  these  protections,  disease  germs 
do  gain  entrance  into  the  body  under  favoring  conditions. 

A  proper  system  of  ventilation  must  take  account  of  this  group  of 
facts,  and  must  ensure  that  the  general  movement  of  the  air  of  every 
inhabited  room  shall  be  downward.  This  makes  it  essential  that  the 
foul-air  outlet  of  every  room  should  be  at  the  floor  level.  And  it  is  best 
that  the  fresh-air  inlet  shall  not  be  in  the  floor.  It  is  not  well  either,  as 
a  rule,  that  the  external  source  of  fresh  air  shall  be  at  the  ground  level, 
because  of  the  liability  to  take  in  injurious  dust. 


Causes  of  Movement  of  Air ,  and  Pates. 

3.  In  cne  third  group  the  most  important  fact,  with  reference  to 
natural  ventilation,  is  this — that,  except  as  caused  by  fans,  blowers,  and 
other  mechanical  means,  movements  of  air  result  from  differences  in 
weight  of  air  at  different  temperatures,  warm  air  being  expanded  air,  and 
therefore  lighter  than  cold  air,  which  is  denser, — in  other  words,  heavier. 
Accordingly,  warm  air  rises  when  its  place  is  supplied  by  colder  air;  and 
cold  air  tends  to  fall  in  under  and  to  displace  warmer  air.  The  rate  of  this 
movement  of  air  depends  upon  the  amount  of  the  difference  in  the  tem¬ 
peratures  of  the  two  bodies  of  air,  and  upon  the  height  of  the  two  oolumns 
of  air — the  displaced  and  the  displacing  oolumns  of  air.  I  have  here  a 
table,  taken  from  Parkes’  Hygiene,  stating  the  rate  of  movement  of  air 
under  different  conditions  of  temperature  and  height  of  column.  I  will 
not  undertake  to  read  the  entire  table,  but  will  merely  state  a  few  of  the 
conditions  and  resulting  rates  of  movements. 


VENTILATION. 


cxxxi 


Table  to  show  the  Velocity  of  Air  in  linear  feet  per  minute.  Calculated  from  Mont¬ 
golfier's  formula;  the  expansion  of  air  being  taken  as  0.002  for  each  degree  Fahren¬ 
heit ,  and  one-fourth  being  deducted  for  friction.  ( Round  numbers  have  been  taken.) 


Difference  Between  Internal  and  External  Temperature,  stated  in  degrees  Fah.,  3  to  30  degrees. 


Helgb 

colum 

feet. 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

30 

10 

88 

102 

114 

125 

135 

144 

153 

161 

169 

176 

188 

190 

197 

204 

210 

216 

222 

228 

283 

239 

244 

249 

254 

279 

11 

92 

107 

119 

131 

141 

151 

160 

169 

177 

185 

192 

200 

207 

213 

220 

226 

233 

239 

245 

250 

256 

261 

267 

292 

12 

96 

111 

125 

136 

147 

158 

167 

176 

185 

193 

201 

209 

216 

223 

280 

237 

248 

249 

255 

261 

267 

273 

279 

305 

13 

100 

116 

130 

140 

153 

164 

174 

183 

192 

201 

209 

217 

225 

232 

239 

246 

253 

259 

266 

272 

278 

284 

290 

318 

14 

104 

120 

135 

147 

159 

170 

181 

190 

200 

209 

217 

225 

233 

241 

248 

255 

262 

269 

276 

282 

289 

295 

301 

330 

15 

108 

125 

189 

153 

165 

176 

187 

197 

207 

216 

225 

283 

241 

249 

257 

264 

272 

279 

286 

292 

299 

305 

312 

341 

16 

111 

120 

144 

158 

170 

182 

198 

204 

213 

223 

232 

241 

249 

257 

265 

273 

281 

288 

295 

302 

309 

315 

322 

353 

17 

115 

133 

148 

162 

176 

188 

199 

210 

220 

230 

239 

248 

257 

265 

274 

282 

289 

297 

304 

311 

318 

325 

832 

363 

18 

118 

186 

153 

167 

181 

193 

205 

216 

226 

237 

246 

255 

264 

273 

282 

290 

298 

305 

813 

320 

827 

335 

342 

874 

10 

121 

140 

157 

172 

186 

198 

210 

222 

233 

248 

253 

262 

272 

281 

289 

298 

306 

314 

321 

329 

336 

344 

351 

884 

20 

125 

144 

161 

176 

190 

204 

216 

228 

239 

249 

259 

269 

279 

288 

297 

805 

314 

322 

330 

838 

345 

853 

360 

394 

21 

128 

147 

165 

181 

19? 

209 

221 

233 

245 

255 

266 

276 

286 

295 

304 

313 

321 

330 

338 

346 

354 

361 

369 

404 

22 

131 

151 

169 

185 

200 

214 

226 

239 

250 

261 

272 

282 

292 

302 

311 

320 

329 

338 

346 

354 

362 

370 

378 

414 

28 

134 

154 

173 

189 

204 

218 

232 

244 

256 

267 

278 

289 

299 

309 

318 

327 

336 

345 

354 

362 

370 

378 

386 

423 

24 

136 

158 

176 

193 

209 

223 

237 

249 

261 

273 

284 

295 

305 

815 

325 

835 

344 

853 

361 

370 

878 

886 

394 

432 

25 

189 

161 

180 

197 

213 

227 

241 

254 

267 

279 

290 

801 

312 

322 

832 

342 

351 

860 

369 

378 

886 

394 

402 

441 

26 

142 

164 

183 

201 

217 

232 

246 

259 

272 

284 

296 

307 

318 

328 

338 

348 

358 

867 

376 

385 

394 

402 

410 

450 

27 

145 

167 

187 

205 

221 

237 

251 

264 

277 

290 

302 

313 

324 

335 

845 

355 

365 

374 

383 

392 

401 

410 

418 

458 

28 

147 

170 

190 

207 

225 

241 

255 

269 

282 

295 

307 

319 

330 

341 

351 

361 

371 

381 

390 

899 

408 

417 

426 

467 

29 

150 

173 

194 

212 

229 

245 

260 

274 

287 

800 

312 

324 

335 

347 

357 

368 

378 

388 

897 

407 

416 

425 

433 

475 

30 

153 

176 

197 

216 

233 

249 

264 

279 

292 

305 

318 

330 

341 

353 

363 

874 

384 

394 

404 

414 

423 

432 

441 

483 

31 

155 

179 

200 

219 

287 

253 

269 

283 

297 

310 

823 

335 

347 

358 

3«9 

380 

391 

401 

411 

420 

480 

439 

448 

491 

32 

158 

182 

204 

223 

241 

257 

278 

288 

302 

315 

328 

341 

358 

364 

875 

386 

.:97 

407 

417 

427 

437 

446 

455 

499 

33 

160 

185 

207 

226 

245 

261 

277 

292 

307 

320 

338 

346 

358 

870 

881 

392 

403 

414 

424 

434 

443 

453 

462 

506 

34 

162 

188 

210 

230 

248 

265 

282 

297 

311 

325 

338 

351 

863 

375 

887 

398 

409 

420 

430 

440 

450 

460 

469 

514 

35 

165 

190 

218 

233 

252 

269 

286 

301 

316 

830 

343 

856 

369 

381 

893 

404 

415 

426 

436 

447 

457 

467 

476 

522 

86 

167 

193 

216 

236 

255 

273 

290 

305 

320 

384 

348 

361 

374 

386 

398 

410 

421 

432 

442 

453 

463 

473 

483 

529 

87 

170 

196 

219 

240 

259 

277 

294 

310 

325 

339 

353 

366 

379 

392 

404 

415 

427 

438 

44S 

459 

470 

480 

490 

536 

38 

172 

198 

222 

243 

262 

281 

298 

314 

329 

344 

358 

871 

384 

397 

409 

421 

432 

444 

454 

465 

476 

486 

496 

543 

39 

174 

201 

225 

246 

266 

284 

302 

818 

833 

348 

362 

376 

889 

402 

414 

426 

438 

450 

461 

471 

482 

492 

503 

551 

40 

176 

204 

228 

249 

269 

288 

305 

322 

338 

353 

867 

381 

394 

407 

420 

432 

444 

455 

467 

477 

488 

499 

509 

558 

45 

187 

216 

241 

264 

286 

305 

324 

341 

858 

374 

889 

404 

418 

432 

445 

458 

471 

483 

495 

506 

518 

529 

540 

591 

50 

197 

228 

254 

279 

301 

822 

341 

360 

377 

394 

401 

426 

441 

455 

469 

483 

496 

509 

522 

534 

546 

558 

589 

623 

De¬ 

grees 

Fahr. 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

80 

This  table  is  taken  from  Parkes’  Hygiene,  American  Edition  1884, 
William  Wood  and  Co.,  page  194.  Its  reading  is  easy,  but  may  be  illus¬ 
trated  as  follows:  Suppose  the  height  of  the  shaft  is  10  feet,  and  the 
difference  in  temperature  outdoors  and  indoors  is  3  degrees  (as  in  the  first 
line,  first  two  columns)  then  the  rate  of  movement  of  the  air  is  88  linear 
feet  per  minute.  Suppose  the  height  of  the  shaft  is  14  feet,  and  the 
difference  in  temperature  is  11  degrees;  then  the  velocity  of  the  air  is  200 
linear  feet  per  minute.  If  thirty  persons  in  the  room  are  eaoh  to  have 
2,000  cubic  feet  of  air  per  hour,  all  are  to  have  1,000  cubic  feet  per  min¬ 
ute,  then,  under  the  conditions  named,  the  cross-section  of  the  shaft  must 
have  an  area  of  five  square  feet.  In  praotioe,  however,  it  is  seldom  that 
a  foul-air  shaft  is  not  higher  than  14  feet. 

The  foregoing  rates  are  in  ordinary  straight  shafts  with  no  extra  oause 
of  friotion;  if  the  shafts  are  very  small,  or  the  friction  unusual,  the  rate 
of  movement  is  lessened. 


cxxxii  STATE  BOARD  OF  HEALTH.— REPORT  OF  SECRETARY,  1894 

It  is  a  general  fact, that  must  be  held  in  mind,  that  eaoh  right  angle  in 
a  shaft  reduces  the  velooity  of  the  air  in  that  shaft  one-half. 

Given  the  number  of  proposed  inmates  of  a  room,  the  height  of  the 
shaft,  and  the  difference  of  temperature  between  the  in-door  and  the  out¬ 
door  air,  then  the  sizes  of  inlets,  outlets,  and  shafts,  can  be  computed,  by 
means  of  the  data  which  have  now  been  stated,  allowing  two  thousand 
cubic  feet  of  air  per  hour  per  person. 

In  this  climate  there  is  no  difficulty  in  securing  good  ventilation  in  the 
warmest  weather,  because  then  windows  and  doors  are  usually  open;  nor 
in  the  coldest  weather,  beoause  then  the  difference  in  temperature  is  so 
great  between  the  out-door  and  the  in-door  air  that  very  rapid  movement 
of  the  in-door  air  is  caused  by  permitting  to  be  balanced  against  it  a  col¬ 
umn  of  dense  out  door  air.  The  difficulty  in  securing  ventilation  occurs 
in  the  spring  and  autumn,  when  there  is  little  difference  in  the  tempera¬ 
ture  of  the  in-door  and  the  out-door  air.  The  ventilation  of  every  inhab¬ 
ited  room  should  be  so  planned  as  to  be  susceptible  of  regulation  and 
especially  of  extension  or  expansion,  by  means  of  registers  into  flues  and 
shafts  of  a  size  ample  for  times  of  slight  difference  in  temperature  of  the 
out  door  and  the  in-door  air.  The  calculations  for  sizes  of  inlets,  outlets, 
flues  and  shafts,  should  be  made  upon  the  basis  of  a  very  slight  difference 
of  temperature. 


Each  Boom  Should  Have  Separate  Ventilation. 

One  important  principle  which  is  perhaps  most  frequently  violated  by 
architects,  contractors,  and  builders,  was  stated  by  Prof.  R.  C.  Kedzie  in 
the  first  Annual  Report  of  the  Michigan  State  Board  of  Health,  page  95, 
as  follows:  “For  successful  ventilation  I  oonsider  it  essential  that  the 
foul  air  of  each  room  shall  enter  a  separate  compartment  in  the  ventila- 
ing  shaft,  and  not  one  common  shaft.”  The  old  “Ruttan”  system,  and 
the  “Smead  dry-closet  system”  both  violate  this  very  important  principle. 
Some  of  the  reasons  why  it  is  important  that  the  foul-air  shaft  from  each 
room  shall  extend  separate  and  distinct  to  the  outer-air,  are  as  follows: 
It  is  praotically  impossible  to  so  control  all  the  conditions  that  the  pres¬ 
sure  of  air  into  two  rooms  shall  always  be  the  same;  all  openings  into  one 
room  (except  registers)  may  at  some  time  be  closed,  while  at  the  same 
time  a  window  or  a  door  into  the  other  room  may  be  open;  one  room  may 
be  on  the  side  toward  whioh  the  wind  is  blowing,  while  the  other  room  is 
on  the  side  from  which  the  wind  is  blowing;  in  such  cases  a  oommon 
vent  shaft  is  filled  with  air  from  the  room  into  whioh  the  pressure  of  air 
is  greatest,  to  the  exclusion  of  the  foul  air  from  the  other  room,  whioh  is, 
therefore,  not  ventilated.  An  instance,  at  one  of  the  State  asylums  in 
Michigan,  will  illustrate  another  reason:  foul-air  shafts  from  rooms  on 
both  sides  of  the  building  extended  up  to  the*  attic,  where  they  terminated 
in  that  common  reoeptaole  from  which  a  oommon  shaft  extended  through 
the  roof.  During  a  wind,  a  window  being  open  in  a  room  on  that  side  of 
the  building  on  whioh  the  wind  did  not  blow,  a  current  of  foul  air  was 
found  to  come  down  from  the  attic  through  the  foul-air  shaft  and  go  out 
of  the  window,  there  being  a  constant  circulation  of  foul  air  through  the 
room,  while  the  warm  fresh  air  which  was  supposed  to  enter  the  room 
through  a  transom  was  not  entering;  the  only  air  supplied  to  the  inmate 
of  the  room  being  the  foul  air  from  the  other  side  of  the  building,  which 


VENTILATION. 


CXXXlll 


might  be  not  only  impure  with  produots  of  respiration,  but  also  oontain 
the  germs  of  any  oommunioable  disease  which  like  consumption  might  be 
present  in  the  other  rooms  of  the  asylum.  Such  “baok-drafts”  are  not 
unoommon  in  school  buildings  in  which  this  principle  under  discussion 
is  violated;  and  suoh  “back-drafts”  are  believed  to  be  especially  danger¬ 
ous  where  they  oome  from  excreta  which  is  dry  from  which  germs  of 
disease  may  then  be  detached  and  float  in  the  foul  air. 


In  the  discussion  following  a  paper  by  Prof.  French  of  Hillsdale  and 
this  paper,  Dr.  Baker  said : — I  do  not  believe  in  having  the  heat  from 
steam  pipes  in  the  rooms;  I  think  it  is  a  vicious  system.  If  we  are  to 
have  the  heating  by  steam,  whioh  I  agree  with  the  Professor  is  the  pleas¬ 
antest,  perhaps,  unless  it  is  the  hot  water,  the  steam  pipes  should  not  be 
in  the  room,  but  should  be  where  the  fresh  air,  in  coming  from  out  of 
doors,  shall  pass  over  them  into  the  room;  that  is  called  the  “indirect” 
system.  The  method  of  heating  by  steam,  having  the  coils  in  the  room, 
is  a  vicious  system,  and  there  is  no  good  way  of  ventilating  in  such  a  way 
of  heating.  You  can  smell  the  results  of  it  as  soon  as  you  enter  the  room  ; 
the  exhalations  when  the  pipes  are  cold  are  oondensed  on  the  pipes,  when 
they  are  heated  again,  they  give  them  off;  but  the  main  difficulty  is  that, 
in  that  method  of  heating,  there  is  no  provision  for  fresh  air.  The 
“direct”  method  of  steam  heating  is  vicious,  and  ought  not  to  be 
employed,  as  a  rule,  anywhere.  The  steam  ooils  should  be  outside  of  the 
room,  and  the  fresh  air  should  pass  over  those  coils  into  the  room,  and 
then,  in  the  proper  system,  the  air  at  the  floor  level  is  carried  off. 

Prof.  Delos  Fall ,  Albion. — With  the  direot  system  of  heating,  by 
steam,  the  system  of  ventilation  is  an  extra  affair,  and  must  be  worked 
out  by  itself;  you  have  to  provide  an  extra  plaoe  for  your  air  to  oome  in 
and  go  out.  You  can  provide  that,  of  oourse,  you  can  have  a  plaoe  for 
the  fresh  air  to  come  in  from  outside  of  the  building,  and  you  oan 
have  a  place  for  it  to  go  out  at  the  floor  level,  with  the  ooils  in  the  room ; 
but  the  air  comes  into  the  room  oold  when  its  draft  is  often  dangerous, 
and  I  see  no  way  of  having  a  proper  supply  of  fresh  air  in  the  “direot” 
method  of  steam  heating. 

Mr.  Goodrich ,  Hillsdale — I  would  like  to  ask  if  there  is  much  differ¬ 
ence,  as  far  as  the  heating  and  ventilation  is  concerned,  between  the 
steam  heat  and  the  hot  water  system? 

Dr.  Baker ,  Lansing — In  the  coldest  weather,  there  is  perhaps  an 
advantage  in  having  the  steam ;  but  there  is  a  disadvantage  in  the  spring 
and  fall,  when  one  needs  a  little  heat,  and  not  very  much.  If  you  have 
to  heat  the  pipes  up  to  212  degrees  before  you  get  any  heat,  and  then  all 
at  onoe  you  get  great  heat,  that  is  not  a  very  pleasant  way  to  do.  If  you 
have  the  “indireot”  method  of  heating,  by  means  of  hot  water,  you  have 
the  ideal  system.  It  is  expensive,  perhaps;  but  when  the  fire  is  built 
and  the  water  in  the  boiler  is  heated  a  few  degrees,  the  circulation  com¬ 
mences,  and  the  incoming  air  is  warmed,  little  or  much  as  you  desire; 
that  is  the  great  advantage  of  heating  by  hot  water,  that  the  heat  is  more 
easily  suited  to  the  temperature  of  the  air  in  the  spring  and  autumn 
months.  In  the  coldest  weather,  it  is  an  advantage  to  have  the  hot-water 


cxxxiv  STATE  BOARD  OF  HEALTH.— REPORT  OF  SECRETARY,  1894. 

% 

surfaoe  line  in  the  boiler  below  the  level  of  the  radiator,  and  so  heat  by 
steam;  that  is  a  method  that  is  easily  accomplished  by  simply  lower¬ 
ing  the  water  in  the  boiler;  and  instead  of  passing  the  water  through 
the  coils,  pass  steam  through;  that  can  be  done  in  the  cold  weather, 
and  in  the  spring  or  fall  the  hot  water  can  be  used. 


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